Preparation of 1,1-dicyano ethylene by the pyrolysis of 1,1,3,3-tetracyano propane



Patented July 11, 1950 7 PREPARATION F LI-DICYANO ETHYLENE ;:BY THEPYROLYSIS CYANO PROPANE OF 1,1,3,3-TETRA- Harry Gilbert, Cuyahoga Falls,Ohio, asslgnor to The B. F. Goodrich Company, New York, N.,Y., acorporation of New York 7 No Drawing. Application March 4. 1949, YSerial No. 79,712 j a 11 Claims.

This invention relates to a method for the preparation of 1,1-dicyanoethylene. which method involves the thermal decomposition of 1,13,3-tetracyano propane.

In copending applications of 'Alan E. Ardis, Serial Nos. 785,520,'filedNovember 7, 1947 now Patent Number 2,476,270, and 63,434, filed December3, 1948 now Patent Number 2,502,412, two ,novel'methods'i'or thepreparation of 1,1-dicyano 'jethylene'jare disclosed. Thafirst. methodin- :'volves, the pyrolysis of l-acetoxy-Ll-dicyano ethane to give1,1-dicyano, ethylene and acetic acid, and the second method involvesthe pyrolysis of compoundsof the general formula yields by the thermaldecompositionof 1,1,3,3-,-.

tetracyan'o propane. In addition to l,l-dicyan o ethylene, somemalononitrile is also formed, the pyrolysis reaction proceedingsubstantially as follows:

i reactionprovides a valuable and economi-i cal method for thepreparation of 1,1-dicyano ethylene since the starting material,1,l,3,3-tetracyano propane, is easily prepared by the reaction ofmalon'onitrile and formaldehyde in aqueous -solution.

The precise conditions under which the'thermal decomposition reaction iscarried out arenot strictly critical provided, of course, that theheating'of the1,1,3,3-tetracyano propane be suflicient to causethe'evolution of vapors. The tetracyano propane is! itself thermallyunstable and does not exist in the gaseous formi Vapors containing thedesired 1,1 dicyano ethylene are evolved when l,l,3,3-tetracyano propaneis heated under atmospheric pressure to a temperature just above itsmelting point, thatis, just above 137 C., and accordingly theseconditions are operative. However,- the reaction proceeds very slowly atatmospheric pressures when temperatures belowabout 150 C-uare utilizedand it is therefore desirable that reduced pressures "or highertemperatures, preferably both, be employed, whereupon the thermaldecomposition of the 1,1,3,3 -tetraoyanopropane proceeds quite rapidly.In this connection it has beenpfound that pressures of approximately2;to,;50 mm. of mercury are preferably used while temperatures of from150 C. to;250 C. are especially preferred.

The thermal decomposition reaction maybe carried out in any one of anumber-of dififerent manners. For example one preferred-method consistssimply in heating the 1,1,3,3-tetracy ano propane, a white solid, in adistillation apparatus whereupon vapors of 1,1-dicyano ethylene areformed, and collecting and condensing the resuiting vapors in a suitablereceiver, preferably provided with external cooling means.Alternatively, however, the reaction may be, carried out by passing the1,l,3,3-'tetracyano propane through a heated metal or glass pyrolysistube and condensing the eiiluent vapors or by other methods of thermaldecomposition. When the thermal decomposition is accomplished in theabove manner the product which collects in thereceiver is a mixture of1,1-dicyano ethylene, malononitrile, and in some instances; smallquantities of 1,1,3,3-tetr-acyano propane. The l,l-dicyano ethylene isthen separated from the mixture by utilizing any. of several methods ofseparation. For example; one method of separating the 1,1,-dicyano'ethylene consists in utilizing the tendencyof monomeric I,1-dicyanoethyleneto polymerize on standing or on heating, and allowing it topolymerize,.;or

-' even adding'water to hasten the'polymerization.

An alcohol such as ethyl, propyl or butylalcohol. or the like, is thenadded to the mixture to dissolve the malononitrile and any1,1,3B-tetracyano propane which might be present and'the insolublepolymer is removed by filtering. The polymerized 1,1-dicyano ethylenecan then be depolymerized by pyrolysis, preferably at term peratures of170 C. to 250 C., to obtain very pure reduced pressures. "l,l-'-dicyanoethylene 'distills at 47 C. at 2 mm. and malononitrile 'atf90'C2.at

2 i I A third useful method of separation involves treating the reactionmixture with a conjugated .d-iolefin such as '"butadiener' or:cyclopentadiene which reactswith the 1,1-dicyano ethylene, to

form a solid substituted cyclohexane which can be separated from themalononitrile and impurities and pyrolyzed again at temperatures inexcess of 400 C. to give monomeric 1,1-dicyano ethylene and theconjugated diolefln.

When using either of the latter two methods, it is desirable that the1,1-dicyano ethylene be stabilized against polymerization from the timethat it is formed. This may beaccomplished by using a suitableLI-dicyanqethylene stabilizer (that is, a polymerization inhibitor)which may be mixed with the l,l,3,3-tetracyano propane prior topyrolysis or placed in the receiver for the pyrolysis product. Such astabilizer is also preferably present in the receiver used to collectthe 1,1-dicyano ethylene when it is separated by distillation and whenit is" desired to obtain the monomer by pyrolysis of the polymer or theconjugated diolefin product. suitablestabilizers include phosphoruspentoxide and phosphorus pentasulfide, which are preferred, as well ascertain phenolic materials such as vpicric acid, trinitrobenzene andpyrogallol,' or the stabilization may be accomplished simply by passinga current of sulfur dioxide through the pyrolysis system, the oxides ofsulfur in general being excellent stabilizers for the monomer. Thestabilizer may be present in any desired amount but in general as littleas 0.5 to 3% based on the amount of monomer is suiiicient to preventpolymerization for extended periods of time. i

In addition to the methods disclosed hereinabove, still another usefulmethod for collecting and separating the 1,1-dicyano ethylene exists.This method comprises directing the pyrolysis vapors into a receivercontaining a liquid hydrocarbon such as toluene, isopropyl toluene(pcymene) and the like. 1,1-dicyano ethylene and malononitrile aresoluble in such hydrocarbons while any 1,1,3,3-tetracyano propanepresent is insoluble and can be removed simply by filtering. Uponfractionation of the filtrate, monomeric 1 ,1-dicyano ethylene isobtained in a very pure form. Alternatively, the 1,1-dicyano ethylenecan be recovered from the liquid mixture by cooling; to a temperaturebelow about i-.20 C. whereupon the monomer crystallizes and can beremoved by filtering.

The following specific examples are. intended to illustrate thepreparation of 1,1-dicyano ethylene by the method of this invention,.but are not intended to be construed as limiting the scope thereof, forthere are, of course, numerous possible variations and modifications. Inthe examples all parts are by weight.

Example I 190 parts (1.32 moles) of l,l,3,3-tetracyano propane areplaced in a distilling flask which is connected to a receiver. Thereceiver is cooled to C. and is lined with phosphorus pentoxide toinhibit the polymerization. of the 1,1-dicyano ethylene. TheLLSB-tetracyano propane is then heated to a temperature of 180 C. and ata pressure of 2 mm. until all the starting material is thermallydecomposed. The contents of the receiver are then fractionated through a12 inch column packed with glass helices. 82.5 parts 680%) of monomericLl-dicyano ethylene (Np 1.442, M; P. 8 C., B. P. 47 (1/2 mm.) areobtained. '70 parts of malononitrile are also, obtained.

Example If 90' parts (.65 mole) of 1, ,3,3-tetracyano propane arepyrolyzed as in Example I, utilizing a temperature of 150 C. 44.7 parts(93%) or substantially pure monomeric 1,1-dicyano ethylene (M. P. 8 C.)are obtained.

Example III X perature of 770" C. until all the material is pyrolyzed.The mixture in the receiver is then fractionated into a flask containingphosphorus pentoxide whereupon parts of monomeric 1,1- dicyano ethylene(M. P. 8 C.) are obtained.

ii'mample IV .12 parts of 1,l,3,3-tetracyano propane are heated at atemperature of 180 C. and a pressure of 2 mm. in a distillation flaskand the vapors conducted into a receiver maintained at -70 C. 1.9 partsof monomeric LL-dicyano ethylene and 7.7 parts of polymeric 1,1-dicyanoethylene are obtained. 1 part of malononitrile is also obtained. Thepolymer thus obtained is converted to substantially pure monomer bydepolymerization at temperatures of -C. to 250 C.

Example V 10 parts of 1,1 ,3,3-tetracyano propane are heated at atemperature of 200 C. and a pressure of 50 mm. in a distillation flaskconnected to a receiver containing para-isopropyl toluene (para cymene).The vapors formed are introduced into the receiver below the surface ofthe paraiscpropyl toluene. The monomeric 1,1-dicyano ethylene and themaloncnitrile formed are soluble in the para-isopropyl toluene while thesmall amount of 1,1,3,3-tetracyano propane which is formed by thereversibility of the thermal decomposition reaction is insoluble and isremoved by filtering. The filtrate is fractionated and 2 parts ofmonomeric 1,1 -dicyano ethylene .(M. P. 'Z8 C.) are obtained.

Example VI 10 parts of 1,1,3,3!tetracyano propane maintained in apyrolysis flask are heated to a temperature of 200 C. at 1 mm. pressureand the resulting vapors condensed in a receiver cooled to 0 C.Polymeric Ll-dioyano ethylene is, recovered from the mixture thereceiver by adding ethyl alcohol to the mixture and filtering off theinsoluble polymer. The polymer thus obtained gives the followinganalysis:

Calculated Found C, 51.55% C, 60.03% H, 2.58% H, 2.99%. N.e,5.e0%, N,36.58% 7 When the above examples are repeated utilizing atmosphericpressures and/or temperatures in excess of 250 C., 1,1-dicyano ethyleneis again obtained in good yield although the yields are not as high asthose obtained when the preferred conditions are utilized.

1,1-dicyano ethylene prepared by the method of this invention is veryvaluable for the preparation of polymers and copolymers suitable assynthetic rubbers, synthetic resins and plastics. Furthermore, thepolymers of 1,1-dicyano ethylene are extremely useful in the preparationof spinning solutions from which can be spun fibers and filamentspossessing many valuable properties including great tensile strength andresistance to abrasion and chemical action.

This application is a continuation-in-part of and a replacement for myapplication, Serial No. 775,149, filed September 19, 1947, nowabandoned.

Numerous variations and modifications in the above procedure will beapparent to those skilled in the art and are included within the scopeof the invention as defined in the appended claims.

I claim:

1. The method which comprises heating 1,1,33- tetracyano propane at atemperature and pressure such that vapors are evolved, condensing theeilluent vapors, and separating 1,1-dicyano ethylene from the resultingcondensate.

2. The method which comprises heating 1,1,13,3- tetracyano propane at atemperature in excess of 150 C. whereupon vapors are evolved, condensingthe effluent vapors, and separating 1,1-dicyano ethylene from theresulting condensate.

3. The method which comprises heating 1,1,3,3- tetracyano propane at atemperature of 150 to 250 C. whereupon vapors are evolved, condensingthe eilluent vapors, and separating 1,1-dicyano ethylene from theresulting condensate.

4. The method which comprises heating 1,1,3,3- tetraoyano propane at atemperature in excess of 150 C. and at a reduced pressure whereuponvapors are evolved, condensing the efiluent vapors, and separating1,1-dicyano ethylene from the resulting condensate.

5. The method which comprises heating 1,1,3,3- tetracyano propane at atemperature in excess of 150 C. and at a pressure below 100 mm.whereupon vapors are evolved, condensing the efiluent vapors andseparating 1,1-dicyano ethylene from. the resulting condensate.

6. The method which comprises heating 1,1,3,3- tetracyano. propane at atemperature in excess of 150 C. and in the presence of phosphoruspentoxide whereupon vapors are evolved, condensing the efliuent vapors,and separating monomeric 1,1-dicyano ethylene from the resultingcondensate.

7. The method which comprises heating 1,13,3- tetracyano propane at atemperature in excess of 150 C., at a reduced pressure, andin the presence of phosphorus pentoxide whereupon vapors are evolved, condensingthe efliuent vapors, and separating monomeric 1,1-dicyano ethylene fromthe resulting condensate.

8. The method which comprises heating 1,l,3,3- tetracyano propane at atemperature in excess of 150 C., at a pressure below mm., and in thepresence of phosphorus pentoxide whereupon vapors are evolved,condensing the effluent vapors, and separating monomeric 1,1-dicyanoethylene from the resulting condensate.

9. The method which comprises heating 1,1,33- tetracyano propane at atemperature in excess of 0., at a reduced pressure whereupon vapors areevolved, collecting said vapors in a receiver REFERENCES CITED Thefollowing references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,467,378 Gilbert Apr. 19, 1949.2,476,270 Ardis July 19, 1949 OTHER REFERENCES Ostling: Chem. Abstracts,vol. 15, p. 2829 Diels et al.: Ber. Deut. Chem., vol. 55, pp. 3445-3446(1922).

Conn et al,: Ber. Deut. Chem., vol. 56, 2076- 2080 (1923).

1. THE METHOD WHICH COMPRISES HEATING 1,1,3,3TETRACYANO PROPANE AT ATEMPERATURE AND PRESSURE SUCH THAT VAPORS ARE EVOLVED, CONDENSING THEEFFLUENT VAPORS, AND SEPARATING 1,1-CICYANO ETHYLENE FROM THE RESULTINGCONDENSATE.